The present invention relates to an electronic musical instrument in which plural tones can be simultaneously generated.
A conventional electronic musical instrument for giving a monotony performance, that is, a synthesizer, is usually so constructed that it comprises a keyboard circuit and a musical tone forming section arranged so as to be controlled by a scale tone voltage signal obtained therefrom. The keyboard circuit comprises a series-connected resistance circuit formed by plural resistances connected in series and connected to an electric source, as well as plural key-switches arranged to be closed by the keys of a keyboard and interposed between connecting points of the foregoing resistances and a single common output terminal thereof. The musical tone forming section includes a single VCO, so that by respective scale tone voltage signals obtained at the output terminal of the keyboard circuit by closing of the respective key-switches, the VCO is controlled to generate musical tone signals.
This conventional instrument operates in such a manner that, as is well-known in the art, when two or more keys are simultaneously depressed, a single scale tone voltage signal on the lower or lowest side of the series-connected resistance circuit is taken out with priority to generate a single tone, and thus it is impossible to generate plural tones simultaneously.
Plural tones can be generated simultaneously by an arrangement in which there are provided plural keyboard circuits for generating scale tone voltage signals corresponding to respective keys, and plural musical tone forming sections connected to respective output terminals thereof. This arrangement, however, is disadvantageous in that it makes the instrument have a larger number of component parts, be larger in size, and higher in price. In addition, the practical use causes such inconvenience that the adjustment of oscillation frequencies of the respective VCOs is not easy.
Accordingly, the present invention has the object to provide such an electronic musical instrument that plural tones can be simultaneously generated by controlling a comparatively small number of musical tone forming sections by a keyboard circuit of comparatively simple construction.
Another object of the present invention is to provide such an electronic musical instrument that when plural keys are depressed in sequence with a time lag, a portamento effect tone is generated to give variety to the performance of the instrument which otherwise is liable to be monotonous.
A further object of the present invention is to provide such an electronic musical instrument that unintentional generation of a portamento effect tone caused by closing, with a time lag, of the key-switches at the time of simultaneous depression of the plural keys is prevented. In addition, the invention prevents the chattering phenomenon of key-switches, from which an unstable operation is caused and noise is generated.